Synthesis of biobased polyols using algae oil for multifunctional polyurethane coatings

Renewable sources – namely, algae oil and diacids – were used for the synthesis of alkyd (ALK) and polyesteramide (PEA) polyols. The prepared polyols were characterised by Fourier transform infrared and nuclear magnetic resonance techniques and size exclusion chromatography analysis. After reaction with diisocyanate, polyols were converted to polyurethane (PU) coatings, which were then characterised by X-ray diffraction, differential scanning calorimetry and thermogravimetric analysis. The biocidal activities of the films were evaluated against Gram-negative (Escherichia coli ) and Gram-positive bacteria (Staphylococcus aureus) by using the turbidity method as well as by observation of film degradation or biofilm formation by bacteria on the surface of a metal tray by using scanning electron microscopy. The PUs obtained using ALK and PEA showed better antimicrobial properties compared with PUs based on algae oil fatty amide (AOFA), monoglyceride (MG) and even an uncoated mild steel (MS) panel. The anticorrosion properties of PU coatings were evaluated by the potential dynamic polarisation (PDP) method in a 3·5 wt% sodium chloride (NaCl) corrosive media. All coated samples (ALK and PEA) showed good barrier properties against corrosion compared with AOFA, MG and the uncoated MS panel. The prepared algae-oil-based PU coatings showed better chemical, mechanical, water-repellent, antimicrobial, anticorrosive and thermal properties.